feat(build): add jq to Docker image

[danshilm]

Adds jq, which is super useful to parse JSON from webhook requests, to the Docker image.

[TheCatLady]

So, adnanh/webhook can already parse JSON payloads: https://github.com/adnanh/webhook#multipart-form-data 🤔

I would prefer to keep this image as minimal/tiny as possible, but I'm not completely against adding jq if there's sufficient justification for it.

[danshilm]

jq comes in very handy for me when I have to parse JSON to make API requests in my bash scripts since unfortunately not all values required to make those API requests are available in the initial payload that the webhook server handles.